The present invention is directed to a method for generating a sinusoidal line AC voltage from a DC voltage that, for transmission via a high-frequency transformer, is converted into alternatingly successive upward and downward square-wave voltage pulses having a respectively maximum pulse-duty factor of 50 percent and a constant pulse frequency, being tapped with a respectively given, fixed pulse-duty factor after the transmission and being then filtered. The present invention is also directed to a circuit arrangement for the implementation of the method.
With the use of computers, there is an increasing requirement for reliable operation of interruption-free power supplies even given network disturbances, for example line outage or line undervoltage. Currently, uninterrupted power supplies are manufactured as power supplies integrated in the computer or as preceding auxiliary devices. The preceding auxiliary devices contain an inverting rectifier that generates an AC voltage from a DC voltage given line errors.
Such an inverting rectifier is known, for example, from the U.S. Periodical IEEE Transactions on Power Electronics, Vol. 3, No. 4, October 1988, pages 406 through 411. The inverting rectifier is essentially composed of a transformer having two primary switches switched in push-pull and two secondary switches switched in push-pull and that is also composed of a filter circuit at the secondary side of the transformer. Both the primary switches as well as the secondary switches are respectively switched with a constant pulse-duty factor of 50 percent. The sinusoidal output voltage is obtained in that the secondary switches switch with a sinusoidally varying phase shift compared to the primary switches.
German Published Application DE 39 12 941 discloses a voltage supply device having a corresponding inverting rectifier. The inverting rectifier is composed of a square-wave converter, of a transformer, of a power converter and of a filter means. The power converter and the filter means are designed for generating three line AC voltages The component parts for generating a line AC voltage are therefore present three times in these component parts. The functionings of the component parts for generating a line AC voltage, however, are respectively identical the difference is only in the respective chronological control.
For generating the individual line AC voltage, the square-wave converter has switch means controlled push-pull. The switch means convert a DC voltage into alternating successive upward and downward voltage pulses. The voltage pulses immediately follow one another and each respectively lasts for the same time without variation. The voltage pulses are conducted via the transformer. Following the transformer, the transmitted voltage pulses are subjected in the current transformer to a respectively prescribed chronological duration. The chronological duration of the individual taps is different for every transmitted voltage pulse. The underlying change in the chronological duration of the tap corresponds to the sinusoidal change of the sinusoidal line AC voltage to be generated. The voltage pulses acquired at the tap are then converted by the filter means into the sinusoidal line AC voltage to be generated.
One disadvantage of the above-described inverting rectifier is that current is constantly drawn from the DC voltage source and the DC source is thus constantly loaded since no return of energy into the voltage source is undertaken during the generation of the sinusoidal line AC voltage.